The present invention relates to an open-type magnetic circuitry of loudspeaker, and more particularly to a magnetic circuitry of loudspeaker enabling quick dissipation of internal heat produced during operation of the loudspeaker, so that the loudspeaker is free of accumulated heat and deformed or separated diaphragm due to operation for a prolonged time and could always maintain good sound quality.
As a component in a stereo sound system, a loudspeaker, or speaker, is actually a transducer that converts electrical energy into sound energy. Therefore, the loudspeaker has considerable influence on the quality of sound produced by the stereo sound system. Generally, a magnetic circuitry for a loudspeaker to operate includes at least a magnet, a voice coil, a diaphragm, a frame, an upper yoke (or ring-shaped yoke), and a lower yoke (or T-shaped yoke). According to a position of the magnet in the loudspeaker, loudspeakers are divided into two types, namely, internal-magnet and external-magnet speakers.
FIG. 1 is a sectioned side view of a conventional internal-magnet loudspeaker. The magnetic circuitry for this type of loudspeaker mainly includes a substantially U-shaped yoke 60 made of a magnetic conductive material, or soft iron, with an upper edge of the U-shaped yoke 60 bent radially inward, a magnet 61 positioned in the yoke 60, a bobbin 63 in a predetermined length provided above the magnet 61 to project from the upper edge of the yoke 60, and a voice coil 62 wound around the bobbin 63 to connect to a root portion of a diaphragm 64 without contacting with the magnet 61 at all. When the loudspeaker operates in a normal manner, the voice coil 62 is caused to move back and forth and therefore forces the diaphragm 64 to move back and forth at the same and thereby produces sound waves. Such continuous vibration (or work) of the voice coil 62 produces heat that accumulates in the U-shaped yoke 60. Since the voice coil 62 of an internal-magnet speaker is in a space enclosed by the U-shaped yoke 60 and a damper 65, the produced and accumulated heat is not easily diffused to dissipate. When the internally produced heat accumulates to a certain extent, it results in magnetic attenuation, particularly when a neodymium alnico magnet is used for the loudspeaker, and accordingly deteriorated sound quality. Another problem with the internal-magnet loudspeaker concerns the diaphragm 64. The diaphragm 64 is made of a resin material that tends to become softened at a raised temperature. A softened diaphragm 64 has shortened usable life and results in noises and undesired resonance during sound production. All these factors result in difficulties in designing a high-power loudspeaker and increased manufacturing cost thereof.
FIG. 2 is a sectioned side view of a conventional external-magnet loudspeaker. The magnetic circuitry for this type of loudspeaker includes a lower yoke 70 substantially in the shape of a reverted letter xe2x80x9cTxe2x80x9d, a bobbin 71 formed from a central vertical portion of the T-shaped lower yoke 70, a voice coil 72 wound around the bobbin 71, a ring-shaped magnet 73 put around a lower part of the bobbin 71, and a damper 75 and a diaphragm 74 sequentially provided above the voice coil 72. As in the case of the internal-magnet loudspeaker, the voice coil 72 is in a space enclosed by the ring-shaped magnet 73 and the damper 75, resulting in accumulated heat in the magnet 73 that in turn causes magnetic attenuation and softened diaphragm 74 to increase difficulties in designing a high-power loudspeaker and manufacturing cost thereof.
It is therefore a primary object of the present invention to provide an open-type magnetic circuitry of loudspeaker that eliminates the problem of accumulated heat in a closed internal space of the loudspeaker.
Another object of the present invention is to provide an open-type magnetic circuitry of loudspeaker that allows a user to see from outside of the loudspeaker an entire working process of the magnetic circuitry, that is, the movement of the voice coil, giving the loudspeaker a novel appearance showing a high-tech touch.
To achieve the above and other objects, the open-type magnetic circuitry of loudspeaker of the present invention includes a lower yoke having a central portion upward projected to form a bobbin, a magnet positioned on top of the bobbin, a voice coil wound around the bobbin and the magnet, and a diaphragm connected at a root portion to the voice coil. The magnetic circuitry of loudspeaker is characterized in that the lower yoke is provided at an upper side surrounding the bobbin with a plurality of radially equally spaced supporting posts, a top end of which being higher than at least a bottom side of the magnet, and that a ring-shaped upper yoke having a central hole is covered onto the top end of the supporting posts, such that heat produced by the voice coil during working could quickly dissipate via a space between the upper and the lower yokes. Since no heat would accumulate in the loudspeaker, the loudspeaker could always maintain good sound quality.